Such a coupling piece is known from DE 102 38 895 A1. When loading containers on board ships, the containers are first raised with a spreader on the pier and the corner fittings are then hung into the lower corner fittings of the raised container. The container is subsequently lifted on board and deposited there on a container already standing on deck. The coupling pieces now interlock with the upper corner fittings of the lower container. The container is now secured against slipping and being lifted off; however, it may be additionally secured by means of lock rods.
The coupling piece shown in DE 102 38 895 A1 has a locking lug directly to the side at the lower coupling projection. One problem with this coupling piece is that it can be inserted in two different orientations, namely rotated by wherein about the vertical axis. It is therefore explained in the document that it is very important that the locking lug of the coupling pieces located on one front side of the container point in the same direction to make it possible to satisfactorily unlock and lock the container. It is possible that all four locking lugs point in the same direction or the locking lugs on one front side point in one direction and the locking lugs on the other front side in the other direction. As was mentioned, the only thing that is important is that the locking lugs on one front side always point in the same direction. Reference is made in this respect to DE 102 38 895 A1.
Securing means that prevent the coupling pieces from being inserted such that the locking lugs on one side point in different directions are not shown in DE 102 38 895 A1. Correct insertion of the coupling pieces is rather made the responsibility of the stevedore. Thus, incorrect operation due to human failure is not ruled out.